You can tell I use my “half sheet pans” every day….I’d say they are well “broken in”, as they certainly are a workhorse in our kitchen. I love having lots of them so I can always grab a clean one….line it with a pre-cut parchment sheet and I am ready to go for roasting veggies, baking cauli rice…so handy! These are made of aluminum…and I am not a fan of that…BUT I always line them with parchment or a silpat so food is never in direct contact with the aluminum. The restaurant grade ones are almost always aluminum for its light weight and heat conductivity.
This is a handy graphic for sheet pan sizes.